Speak with the innkeepers of Stormwind, Ironforge, and Darnassus, as well as Talvash del Kissel in Ironforge. Perform the tricks they ask of you in exchange for the treats they offer.
Return to Jesper at the Stormwind Orphanage with a Darnassus Marzipan, Gnomeregan Gumdrop, Stormwind Nougat, and Ironforge Mint.
I want to go trick-or-treating, but I can't because I'm sick. If you go for me, I'd trade you the candy you get for some I already have! I think you'd like this candy - it makes you turn into things both funny and scary!
Each of the innkeepers in the big cities have candy they give for Hallow's End - talk to them and do the tricks they ask for! Also, a little gnome named Talvash in Ironforge is handing out candy as well. When you have all the candy, bring them back to me here!
